1. Field of the Invention
The present invention relates to an actuator for moving an operative means of a valve between open and closed positions. Additionally, the invention relates to a pilot assembly for manipulation of the operative means in response to pressure variances.
2. Description of the Prior Art
Valve actuators are utilized to manipulate an operative means, such as a stem, of a valve mechanism on a flow line into open and/or closed position in response to control pressure variation. Normally, such actuators comprise a shaft and a fluid activated mechanism in association therewith which, upon activation thereof by variation in control pressure, causes longitudinal movement of the shaft to shift the valve head in relation to its seat to move the valve to open or closed position. Venting of control pressure within the actuator will cause a subsequent longitudinal shifting of the shaft and the valve head to a second position to the other of open and closed position. Such actuators and valves are frequently utilized in safety systems used in conjunction with the drilling, completion and production of oil and gas wells. They are also utilized in natural gas transmission lines, and the like.
Valve actuators may be classified into two basic classifications: (1) those which are of necessity manipulatable only in response to pressure variation supplied through a pressure source other than that directly within the flow or transmission line; and (2) those which are manipulated by control fluid variance, the control fluid being tapped directly from the flow or transmission line itself. Because it is impractical to supply an independent fluid source for actuator control purposes on long and isolated transmission lines on valves selectively placed along the flow or transmission line in isolated environments and areas, an actuator as described in the second classification above is preferably utilized; namely, one which is responsive to variance in the flow or transmission line pressure itself to manipulate the valve between open and closed position. These actuators, sometimes referred to as "in-line" actuators, are well known in the prior art and may have a fluid transmission line exterior of the actuator housing and connected with the flow or transmission line either upstream or downstream of the valve to be manipulated by an external pilot. This feature is somewhat disadvantageous because it is cumbersome and is subject to vandalism or unintentional damage to render the actuator inoperative or unsafe.
During the transmission of liquid or gaseous fluids within a flow or transmission line, it often occurs that pressure within the line will vary either above and/or below the normal operating pressure because of, for example, a break or leak in the line either upstream or downstream of the valve manipulated by the actuator, or because of clogging of contaminant, such as paraffin and scale within the line, which may become sufficient to cause a pressure increase within the line beyond the normal operating pressure range. Therefore, an actuator should be utilized which is responsive to either an increase or a decrease in line pressure beyond normal operating pressure range to manipulate the valve and isolate the line upstream and downstream thereof. Heretofore, such an "in-line" actuator has been technically and commercially successful only on a comparatively limited scale because the design of such prior art actuators has, of necessity, required the utilization of multi-valve means in the actuator which could be manipulated to open and close flow passageways therethrough to cause the actuator to shift the valve operative means to move the valve to one of open and closed positions. Because of substantial friction caused by pressure differentials, the prior art valving means utilized in such an actuator are somewhat unreliable, cumbersome and inaccurate in sensing pressure. The present invention overcomes these obstacles common to the prior art by providing an actuator having a pilot assembly therein which utilizes a plurality of normally free traveling spherical members in association with pilot means therein having seal bores for sealing engagement thereon of one of said spherical members, which is caused to seek and seal thereon. The sealed spherical member subsequently is easily wipable off of its seal bore, even though substantial differential pressure may be encountered across the spherical member when on its seal seat, to permit fluid transmission therethrough by manipulation of a spool within the pilot assembly which itself is responsive to valve body pressure. The sphere has an inherent mechanical advantage determined by the relationship of sphere-to-port diameters and is frictionless inasmuch as the ball rolls off of its port.
There may be need, from time-to-time, to remove a pilot from an actuator for repair or replacement purposes while the actuator is in operation on a flow or transmission line. The valve must be shifted to closed position on the flow line and, heretofore, necessitating considerable down time. This obstacle is overcome in the present invention by providing a means for quickly, but safely, removing the pilot assembly from the actuator while well or flow line pressure is held within the actuator and is not vented to atmosphere. The present pilot assembly may be repaired or replaced and quickly reinserted into the actuator without loss of control of flow line or well pressure through the actuator.
As an actuator is broken down on location to repair or replace components, it is possible for parts of a prior art actuator to be threadedly disengaged from companion parts while well or flow line pressure within the actuator is still "live" and within the actuator. To avoid pressure and disengaged parts from being explosively discharged into the face of a service man, or around the environment exterior of the actuator, the present invention provides O-ring and bleed port means operative in conjunction with the threads at part connections to carefully and controllably vent live pressure to atmosphere and directly away from the service man before any threaded part becomes disengaged sufficient for the part and pressure to become explosively discharged.
Also in association with the disassembly of an actuator on location, there is need to provide a means for controlling flow line or well pressure within a minimal number of actuator components. The actuator of the present invention permits almost complete disassembly of its respective component parts while the flow line valve is in closed position by providing a resilient seal or "fire seal" and seat which maintains flow line pressure on only the actuator stem and housing while other component parts may be completely disassembled therefrom for repair or replacement purposes. The present actuator may be completely disassembled for repair purposes without bleeding off the entire pipe or flow line, thus avoiding considerable flow line down time.
Many prior art actuators are not considered to be "fail safe", i.e., they do not incorporate power springs or other energy storage devices in the event of substantial loss of valve body pressure. The present actuator is entirely "fail safe" in its entire operating sequences, as will be described in detail hereinafter.
When prior art actuators sense an improper pressure environment within the flow line, the valve is closed and well or flow line pressure is vented to atmosphere through a bleed port, causing considerable pollution of the environment. The present actuator is completely non-polluting during all valve manipulation modes without venting fluid to atmosphere. This inventive feature is attributable to the incorporation of a pilot assembly which will shut the gate valve upon variation in well or flow line pressure by equalizing pressure across a piston contained within the actuator, as opposed to venting operating pressure to the atmosphere.
Prior art actuators have been provided which, after sensing a high pressure environment above normal flow line pressure and which trip the actuator to manipulate the valve to closed position, are not selectively functional thereafter to open the valve if pressure returns to within normal operating range. The present actuator overcomes this obstacle by providing a means for selective resetting of the actuator pilot to permit the actuator to be set to open the valve upon subsequent decrease of pressure from a high pressure environment to normal operating range. Alternatively, the actuator also may be set to prevent the valve from reopening when pressure is returned to normal after encountering a high pressure environment.
Previous actuators have been designed to be responsive to a pressure condition below normal operating pressure to manipulate the valve to closed position. Prior art actuators are typically non-automatically resettable after a low pressure condition is sensed and the flow or well line subsequently returns to within the normal operating range. However, none are known to be available to close the valve upon detection of a low pressure condition, as well as upon detection of a high pressure condition, and are selectively resettable after encountering a high pressure condition. These features are very practical and quite important because gate and similar valves utilized on flow lines normally seal on the downstream seat in the valve body. Differential pressure thus moves the gate to the far or downstream seal and pressure under the actuator bonnet in a closed gate valve is always defined as upstream pressure. If the flow line ruptures just downstream of a given flow line valve, pressure in that valve body will go to substantially zero and the actuator will sense a low pressure condition and close the valve. When the valve closes, pressure will return to within normal operating range under the bonnet and the pilot in the actuator will be urged to clear and open the valve. However, the present actuator is non-selective in resetting after sensing a low pressure condition. This feature is done internally and completely within the actuator without requirement of any mechanical means, such as detent pins or the like. Since the present actuator is fail safe, the valve automatically closes upon sensing a low pressure condition and will remain closed until manually reopened.
If an actuator is responsive to a pressure condition above the normal operating range, such that the valve is manipulated to closed position, and flow line pressure is contained within the actuator, the service man could not apply sufficient force manually through the actuator piston stem because of the increased well or flow line pressure exerted on the stem. The present invention provides a means for manually resetting the actuator after sensing a high pressure environment so that flow line pressure will again activate the pilot to cause the actuator to open the valve.
It occurs frequently that it is necessary to calibrate the pilot assembly of an actuator so that the valve on the flow line is manipulated to open and closed position at pressures above and below the originally set normal operating range. The present pilot assembly provides an easy and readily accessible means for calibration by providing a means thereon for receipt of a hand pump which simulates well or flow line pressure. In conjunction with a gauge mechanism inserted within the pilot assembly, the pilot is caused to mimic the actuator trip and reset modes by application of pressure through the hand pump to calibrate and adjust the pilot assembly, at pressures reflected on the gauge.
Other advantages and features of the present invention will be readily understandable from a reading of the drawings, the specification and claims, which follow.